Electronic devices such as mobile phones use a touch sensitive switch. Such a touch sensitive switch may comprise a display panel such as liquid crystal panel and a pressure sensitive or capacitance type input device. Such touch sensitive switches tend to have a shorter stroke than ordinary mechanical switches. Users sometimes cannot perceive such a short stroke. Hence, developments have been made to provide touch panel devices that can produce vibration or other mechanical movements in concert with a push-down operation by a user so that the user can recognize that their push-down operation was actually made.
Haptic feedback can be generated by various conventional driving sources including a piezoelectric actuator, as described in Japanese Patent Application Publication No. 2010-157037, and an electromagnetic actuator, as described in Japanese Patent Application Publication No. 2006-146611. These actuators are disposed on non-displaying areas of a display panel so as to provide vibration without preventing a user from viewing displayed images on the display panel. Haptic feedbacks can also be provided by other conventional configurations, such as a structure configured by stacking a liquid crystal panel, touch panel, and haptic panel, as described in Japanese Patent Application Publication No. 2011-2926. A haptic actuator can be disposed beneath a liquid crystal panel, as described in Japanese Patent Application Publication No. 2010-152889.
In such conventional haptic feedback devices, in response to a user's pressure contact with a touch panel, an actuator is configured to deform such that the deformation can be conveyed from the touch panel to the user's finger so as to provide the user with a sense that the user made sufficient contact with the touch panel. An input signal to such an actuator can be a simple sinusoidal signal or square wave signal. A special signal such as a kick-in pulse or braking pulse also can be used as an input signal, as described in Japanese Patent Application Publication No. 2010-287231. An actuator signal is also input to an actuator to cause the entire panel to vibrate and operate as a speaker for reproducing a recorded sound of music or voice.
However, in those conventional haptic mechanisms described in the above references, a haptic actuator is disposed on the bottom or rear surface of a heavy liquid crystal panel or touch panel. This arrangement requires an actuator to generate a large actuator force and displacement in order to provide sufficient haptic effects. To achieve such a large actuator force and displacement, a high voltage input needs to be applied. Such a high voltage is difficult to use in electronic devices such as mobile phones. Moreover, an actuator is needed separately from the liquid crystal panel and touch panel. Therefore, the resulting display devices become thicker and cannot be made thin.